Why does a chimney leak even when the flashing looks intact?
A chimney leak can come from the masonry, the mortar, the flashing or the sealant, and the leak can appear far from the true source. The flashing looks intact from the ground, but a lifted step or a cracked joint at the masonry lets the water through.
Water runs down the chimney face and seeps into cracks in the mortar, then along the flashing line. From the ground the stain can look like it is coming from the roof, while the path runs through the brick or stone.
A crew checks the masonry, the mortar and the flashing together. A repair that addresses only one of the three will often leak again through the other, which is why the crew tests all three before deciding.
What do the step and counterflashing do?
Step flashing is a series of metal pieces laid along the sloped sides of the chimney, each overlapping the one below. Counterflashing is set into the masonry and sits over the step flashing, so water runs down the chimney face onto the roof and not into the joint.
The two work together. Step flashing takes the water running down the roof slope, and the counterflashing keeps water from running down the masonry and behind the step. If either one fails, the water finds the joint.
The metal must be laid in the right order and with a clean fall. A step laid backward will catch water and push it inward, even when the metal is sound and the sealant is fresh.
Can a chimney flashing be repaired without rebuilding the chimney?
Often yes. Flashing faults are usually limited to the metal, the sealant or a few mortar joints, and these can be reset or renewed without rebuilding the chimney. Severe masonry damage may need a mason, and the crew says so on the visit.
A crew can reset steps, renew counterflashing and replace sealant on a chimney in good structural condition. The repair stays on the roof and the flashing, and the chimney stands as it is.
If the masonry is crumbling, the mortar has gone deep or the chimney is out of plumb, a flashing repair will not hold for long. The crew explains the limit and suggests a mason, and it does not promise a result the masonry cannot give.
What should I check on a chimney before the rain season?
Check the sealant at the top of the counterflashing, look for cracks in the mortar at the roof line and check the ceiling near the chimney for a stain. These are the points where a chimney leak usually begins, and each can be checked from a safe position.
From the ground, look at the chimney top and the roof line for cracked mortar, lifted metal and missing sealant. Note any change since the last season and any stain in the rooms near the chimney.
Do not climb onto the roof to check. A crew can make the check on a dry day and report what it finds, so the homeowner has a list before the rain starts.
What affects the scope of a chimney flashing repair?
The scope depends on the number of sides that are failing, the condition of the masonry and the mortar, the pitch of the roof at the chimney and the access. The price is explained and approved before any work starts, and no figure is printed on this page.
A chimney on a steep slope needs more care to reach the uphill side, and the crew plans the safety equipment before the work. A chimney with failed flashing on two sides takes more time than one with failed sealant at the top only.
Where the masonry needs work, that is a separate line in the scope. The homeowner can then decide whether to have the flashing reset now, the masonry repaired first or both in a planned order.
